docs: def quaternion_conjugate(quaternion):
      """Return conjugate of quaternion.
  
      >>> q0 = random_quaternion()
      >>> q1 = quaternion_conjugate(q0)
      >>> q1[3] == q0[3] and all(q1[:3] == -q0[:3])
      True
  
      """
      return numpy.array((-quaternion[0], -quaternion[1],
                          -quaternion[2], quaternion[3]), dtype=numpy.float64)